Oxygen on Rosettas Comet?

Ah, Rosetta, everyone’s favourite comet orbiter. The European Space Agency spacecraft that made a splash when it launched a lander onto the surface of Comet 67P is continuing to gather scientific data about its target, and today researchers announced an unexpected exciting discovery: molecular oxygen.

Rosetta’s ROSINA instrument—a mass spectrometer—detected O2 in the icy body’s coma, the cloud of gas and dust and other space stuff around Comet 67P/Churyumov-Gerasimenko. More exciting still, the researchers behind the find, which was published Wednesday in Nature, reckon the O2 is “primordial” oxygen, i.e. that it came from the cloud of molecules from which our Solar System was formed.

In a phone call, lead author André Bieler explained the team found a strong signal of oxygen early on in the Rosetta mission. “But we were so surprised that we initially didn’t know exactly what to do, or why it would be there, and what to do with it, so we decided to just keep monitoring for a while and see what happens.”

So why is it such an exciting find? Oxygen is the third most abundant element in the Universe, but while it’s been detected on some icy bodies in the Solar System, such as planets’ moons, it’d only ever been found in two interstellar clouds, and never in a comet. “No one was expecting it to be there,” said Bieler of the team’s finding.

The researchers observed 67P’s coma from September 2014 to March 2015 and saw a mean value of 3.8 percent molecular oxygen. What’s most important, however, is that this didn’t change as the comet continued onward and approached the Sun. Bieler explained that if the oxygen was only on the surface of the comet, they would have seen a decrease in the ratio of oxygen as the comet burned up and lost gas.

They write that “the preferred explanation of our observations is the incorporation of primordial O2 into the cometary nucleus.”

The presence of this oxygen in the comet’s nucleus suggests it was there when the comet was formed—and was therefore present in the molecular cloud that birthed the planets (as comets are basically leftover material).

“I think we have to kind of rethink our models.”

This adds to our knowledge of the early days of the Solar System—or at least questions it. “Current Solar System formation models do not predict conditions that would allow this to occur,” the authors note.

“One implication is that the accretion [the coming-together of cosmic dust to form the comet] had to be pretty gentle in order for the O2 in the ice to survive,” Bieler explained. “Otherwise I think we have to kind of rethink our models.”

Next, Bieler said they’d like to look at the southern hemisphere of 67P; these new measurements come from the northern hemisphere, as that side facing the Sun (Rosetta is powered by solar arrays). In the future, he said we should also look at other comets for comparison. The Rosetta mission is of course unique in its close targeting of a comet, and previous cometary missions haven’t had the technology capable of detecting oxygen.

The new paper is an example of one of the major scientific aims of the Rosetta mission: using the comet as something of an interstellar time capsule to explore the early days of our own Solar System.